Ltjdwig schon



L.- SCHUN. LhiflTRlCAL CONNECTION.

APPLICATION FILED FEB. 20, I912 Patented Aug. 1, 1916.

UNITED STATES PATENT OFFICE.

LUDWIG- SCHfiN, OF ESSEN-ON-THE-RUHB, GERMANY AS SIGNOR 'IO FRIED. KRUPP .AKTIENGESELLSCHAFT, 0F ESSEN-ON-THE-RUHR, GERMANY.

ELECTRICAL CONNECTION.

Specification of Letters Patent.

Y Patented Aug. 1, 1916.

To all whom it may concern:

Be it known that I, LUDWIG Sondra, residing at Essen-on-the-Ruhr, Germany, a subject of the Emperor of Germany, have invented a certain new and useful Improvement in Electrical Connections, of which the following is a specification. i

In resistances that under ordinary conditions increase with the temperature, the heating of the'resistance as a consequence of a passing electric current will generally cause the current strength to sink therein. In consequence of these circumstances, in separately excited motors for instance, which operate intermittently, and in which the separately excited'field winding, as a rule, remains connected and which in time, while running, will experience a quite considerable heating, the current strength in the field winding as well as the number of revolutions of the motor, may change according to the heat condition of the field winding so considerably, that altogether inadmissible con ditions of operation will be brought about. This disadvantage might for instance be avoided, by making the field winding of a material that practically experiences no change in resistance by heating. The known materials of this kind (consta-ntan for instance) possess, however, such a low degree of conductivity, that their use for making field windings for electromotors is excluded for practical reasons.

The object of the present invention is to provide a connection for eliminating the influence of temperature, which permits of the use of resistances, consisting of the customary kind of material in practical use.

In the drawing is shown a diagrammatical rqprcsentation of one embodiment of a conneclion of this kind.

A separately excited electromotor is indicated by letter A, its field winding W being connected to a network B of constant tension. An auxiliary resistance W is connected in parallel with the field winding W; while still another resistance W is connected with the branch of the circuit where the field winding W and the secondary resistance \V are arranged. As foundation for the invention lies the thought that the undivided current J, which naturally will grow less with increasing heat, will be so divided in the cir- 0111i, branches, that the exciter Winding W will receive an approximately constant current while the other branch current running through the auxiliary winding W is diminished approximately the same amount as the undivided current J.

In the following will be examined the conditions, that have to be fulfilled, to obtain the desired results. If with r, p and R are denoted the magnitude of the resistances corresponding to the windings WV, W and W that exist at a certain moment, we find, according to Kirchhoffs law In this equation, the term lowing and in the claims be referred to simply as substitute resistance. If furthermore the temperature coeflicients of the resistances )V, )V and V are called a, and and the increase in temperature, 1, r and 1: experienced by these resistances at the moment under consideration, the following equations are to be found, when the magnitude of the resistances at the beginning are called 1 p and R If these values are inserted in equation (1) the following is obtained:

fig, ('1 ar)(1 +71") Po 1 57', following:

In the above equation the term found in the denominator of the fraction,

indicates the starting value of the substitute ing value 6 E E 0 r +R of the strength of the exciter current is constant, when the ratio is so chosen, that the increase of the substitute resistance, '5. e. the term within the square brackets, is equal to naught at every moment.

Ordinarily it is suflicient if the current strength 2', of the starting state has the same will be obtained for the increase of the substitute resistance (compare the expression within the brackets in equation 2).

Should now the strength of the exciter current have the same value for both the value as that of the continuous state, as it then as a rule only slightly deviates from this value during the interval. If the increase in temperature of the resistances W, W and W are called respectively 1 1 and r the value {3 3g B m/( 1 m 'Y' mn) m'Y nv/ The current strength for the continuation state may be deduced from equation (2).

starting and the continuation state, the stipulation must be fulfilled, which will be clear from equation (3). This stipulation may also be written in this form which may be regarded as the value of ratio of increase in the substitute resistance dur- I 1 +I3T (4 ing the continuation state. In that case equation (3) may also be written in this form This equation permits one to judge how much the value t] may deviate from naught. If, for instance.

a deviation of 5% were considered permissible for the starting and continuation state in the strength of the exciter current, the value may then deviate from naught by as much together with equation o( +Y m//) and P0( +I m/)- By the use of Kirchhofis law, the existoi? the current strengths appearing in the continuation state. The computation will be especially simple if a material is chosen for the first connected resistance IV that has a temperature coefiicience practically equal to naught. The magnitudes, which may be used, within certain limits, in this computation, should consequently be so chosen, that the sum of the heat quantities produced in the two auxiliary resistances \V and W should be the smallest possible, as it represents a loss, with which the elimination of the influences of the temperature on the current strength in the exciter winding will have to be bought.

I claim:

1. In a. dynamo machine having a field winding excited from a source of constant voltage, electric connections for eliminating the in fluence of the heating of the field winding by the flowing electricity; said connections comprising a circuit branch containing as 0.05, which follows according to equation (3).

In the following will be given a short explanation of the procedure of calculation by the use of the developed designations. The values of 2' 7' 0:, B and Y may be considered as known. Furthermore the increases in temperature 1 1 and 1 may be deliberately chosen within permissible limits. From the stipulated equation (4') said field Winding and a first auxiliary resistance connected in parallel therewith and two conductors connecting said circuit branch with said source of voltage, one of said conductors containing a second auxiliary resistance through which the undivided current runs, the magnitudes and the temperaturecoelficients of said auxiliary resistances, bein so chosen, that any alteration of the Va ue of said resistances due to the heating of the field winding by the flow- 7 ing electricity causes the current. supplied to said first auxiliary resistance to alter approximately at the same rate as the current of said second auxiliary resistance, while the current supplied to said field winding remains approximately constant.

2. In a dynamo machine having a. field winding excited from a source of constant voltage, electric connections for eliminating the influence of the heating of the field winding by the flowing electricity; said connections comprising a circuit branch containing said field winding, and a first auxiliary resistance connected in parallel therewith, and two conductors connecting said circuit branch with said source of voltage, one of said conductors containing a second auxiliary resistance through which the undivided current runs, the magnitudes and the temperature-coeliicients of said auxiliary resistances and their ratio of cooling, being so chosen, that any alteration of the value of said resistances due to the heating of the field winding by the flowing electricity causes the current supplied to said first auxiliary resistance to alter approximately at the same rate as the current of said second auxiliary resistance, while the current supplied to said field winding remains approximately constant.

The foregoing specification signed at Barmon Germany this 30th day of January,

LUDWIG SCHUN. [1 s] In presence of v ALBERT Nnrnu. 

